Micropore forming apparatus and micropore forming method

ABSTRACT

To provide a micropore forming apparatus capable of increasing the amount of interstitial fluid extracted from micropores formed in the skin of a subject. The micropore forming apparatus includes a skin contact part that has a plurality of microneedles for piercing the skin of the subject, and a force exerting part for exerting a force on the skin contact part toward the skin of the subject. The force exerting part is configured so as to exert a force on the microneedles toward the skin at a position at which the microneedles of the skin contact part are to pierce the skin of the subject.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 to Japanese PatentApplication No. 2010-144089 filed on Jun. 24, 2010, the entire contentof which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a micropore forming apparatus andmicropore forming method for forming micropores in the skin of a subjectby piercing the skin with microneedles.

2. Description of the Related Art

There is known art for forming micropores in the skin of a subject bypiercing the skin of the subject via a microneedle tip provided with aplurality of microneedles in order to measure a predetermined component,such a glucose, present in the interstitial fluid of the subject(US2007-0233011). In the piercing apparatus used for micropore formationdescribed in US2007-0233011, after the piercing operation has beenperformed, a measuring device is mounted on the pierced region,interstitial fluid is extracted from the skin, and the glucose contentis then measured.

The piercing device disclosed in US2007-0233011 causes a microneedle tipto pierce the skin of the subject to form micropores therein by drivinga spring-operated piston (chuck array), the leading end of which isprovided with the microneedle tip that has a plurality of microneedlesfor piercing.

The present applicant has proposed a method for calculating (estimating)the glucose time-area under the curve of a subject using the sodium ioncontent of the interstitial fluid (US2011-0124998). In this method,interstitial fluid is extracted from the skin by forming micropores inthe skin of the subject using a piercing device, and adhering, for apredetermined time (for example, 60 minutes or longer), an interstitialfluid collection sheet comprising a gel collection medium onto the skinwhere the micropores have been formed. Then, the amounts of glucose andsodium ions contained in the interstitial fluid are measured, and theglucose time-area under the curve for the subject is estimated based onthe obtained measurements of glucose and sodium ions. In this case, asmall amount of sweat from the skin of the subject is also collected inthe collection medium, in addition to the interstitial fluid extractedfrom the micropores. Since this sweat also contains sodium ions, it isdesirable that a large amount of interstitial fluid is extracted fromthe micropores in order to reduce the influence of the sweat on themeasurement.

SUMMARY OF THE INVENTION

The scope of the present invention is defined solely by the appendedclaims, and is not affected to any degree by the statements within thissummary.

The conventional art does not, however, describe the increase in theamount of interstitial fluid extracted from the micropores.

The present inventors have conducted intensive study of the increase inthe amount of interstitial fluid extracted from micropores formed by thepiercing device. As a result, we have completed the present inventionafter discovering that the amount of interstitial fluid extracted fromthe formed micropores is increased by pressing the microneedles into theskin for a predetermined time after the microneedles have pierced theskin, without quickly retracting the microneedles back into the deviceonce the microneedles have pierced the skin of the subject as in theconventional art.

The micropore forming apparatus of the present invention is a microporeforming apparatus for forming micropores in the skin by piercing theskin of a subject with microneedles, comprising

a skin contact part that has a plurality of microneedles for piercingthe skin of the subject; and

a force exerting part for exerting a force on the skin contact parttoward the skin of the subject;

wherein the force exerting part is configured so as to exert a force onthe microneedles toward the skin at a position at which the microneedlesof the skin contact part are to pierce the skin of the subject.

The micropore forming apparatus of the present invention is configuredsuch that the microneedles that have pierced the skin of the subject arepressed toward the skin by the force exerting part. That is, in thepresent invention, the microneedles are pressed toward the skin of thesubject for a predetermined time after piercing the skin, unlike theconventional art in which the microneedles are quickly retracted intothe piercing device after the microneedles have once pierced the skin ofthe subject. Thus, micropores can be formed in the skin by all of themicroneedles, thereby increasing the amount of collected interstitialfluid and improving the accuracy of the measurements using the extractedinterstitial fluid compared to the conventional art.

The micropore forming method of the present invention is a microporeforming method for forming micropores in the skin of a subject using themicropore forming apparatus, wherein the state of the microneedles beingpressed into the skin is maintained for a predetermined time after themicroneedles have pierced the skin of the subject.

According to the micropore forming apparatus and the micropore formingmethod of the present invention, it is possible to increase the amountof interstitial fluid extracted from the micropores formed in the skinof a subject.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the overall structure of an embodimentof the micropore forming apparatus of the present invention;

FIG. 2 is a perspective view of the internal structure of the microporeforming apparatus shown in FIG. 1;

FIG. 3 is an exploded perspective view of the micropore formingapparatus shown in FIG. 1;

FIG. 4 is a frontal view of the internal structure of the rear cover ofthe micropore forming apparatus shown in FIG. 1;

FIG. 5 is a perspective view of the internal structure of the frontcover of the micropore forming apparatus shown in FIG. 1;

FIG. 6 is a bottom view of the tip insertion member of the microporeforming apparatus shown in FIG. 1;

FIG. 7 is a frontal view of the chuck array of the micropore formingapparatus shown in FIG. 1;

FIG. 8 is a perspective view of the release button of the microporeforming apparatus shown in FIG. 1;

FIG. 9 is a perspective view of the overall structure of the tipreceiver kit provided with a microneedle tip installed in the microporeforming apparatus shown in FIG. 1;

FIG. 10 is an exploded perspective view of the tip receiver kit shown inFIG. 9;

FIG. 11 is a perspective view of the microneedle tip of the tip receiverkit shown in FIG. 9;

FIG. 12 is a cross sectional view on the I-I line of FIG. 10;

FIG. 13 is a top view of the microneedle tip of the tip receiving memberof the tip receiver kit shown in FIG. 9;

FIG. 14 is a perspective view of the tip receiving member of the tipreceiver kit shown in FIG. 9;

FIG. 15 is a bottom view of the tip receiving member of the tip receiverkit shown in FIG. 9;

FIG. 16 is a cross sectional view on the II-II line of FIG. 13;

FIGS. 17(a)-17(c) illustrate the launching principle of a conventionalmicropore forming apparatus;

FIGS. 18(a)-18(c) illustrate the launching principle of the microporeforming apparatus of the present invention;

FIG. 19 shows the pressing time dependence of the glucose transmittance;

FIG. 20 shows the relationship between the length of the time afterpiercing and the glucose transmittance;

FIG. 21 shows the relationship between glucose transmittance and pain;and

FIG. 22 shows the relationship between glucose transmittance andhemorrhage.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments of the micropore forming apparatus and the microporeforming method of the present invention are described in detailhereinafter with reference to the accompanying drawings.

[General Structure of the Micropore Forming Apparatus]

FIG. 1 is a perspective view showing the overall structure of anembodiment of the micropore forming apparatus 1 of the presentinvention. FIGS. 2 through 8 illustrate the structural details of eachcomponent of the micropore forming apparatus 1 shown in FIG. 1. FIG. 9is a perspective view of the overall structure of the tip receiver kitprovided with a microneedle tip installed in the micropore formingapparatus shown in FIG. 1. FIGS. 10 through 16 illustrate the structuraldetails of each component of the tip receiving kit shown in FIG. 9.

The micropore forming apparatus 1 of the embodiment of the presentinvention (refer to FIG. 1) is an apparatus for forming fluid extractionholes (micropores) in the skin of a subject by mounting a sterilizedmicroneedle tip 110 (refer to FIG. 11) so that the microneedles 113 a ofthe microneedle tip 110 abut (contact) the skin of the subject. Then,fluid (interstitial fluid) exudes from the extraction holes in the skinof the subject formed by the microneedle tip 110 and micropore formingapparatus 1, and the extracted fluid is collected by an extractionmedium which is then measured by a glucose concentration analyzer (notshown in the drawings), and the glucose concentration in theinterstitial fluid is calculated, and the AUC is calculated based onthis value. The structural details of the embodiment of the microporeforming apparatus 1 of the present invention are described below withreference to FIGS. 1 through 12.

The micropore forming apparatus 1 forms a plurality of small extractionholes that pass through the stratum corneum of the epidermis but do notreach so far as the blood vessels in the dermis, thereby inducingexudation of interstitial fluid from the extraction holes. The microporeforming apparatus 1 has a main body unit 1 a with a piercing mechanismfor piercing the skin of a subject. As shown in FIGS. 1 through 3, themain body unit 1 a of the micropore forming apparatus 1 has a rear cover10, front cover 20, tip receiver insertion member 30, chuck array 40 asa skin contact part, spring stopper 50, release button 60, injector 70,main spring 80 as a force exerting means (refer to FIG. 3), and aplurality of springs 90 a and 90 b (refer to FIG. 3). Note that theseven members (rear cover 10, front cover 20, tip receiver insertionmember 30, chuck array 40, spring stopper 50, release button 60, andinjector 70) excluding the springs (main spring 80 and plurality ofsprings 90 a and 90 b) are respectively made of synthetic resin. Thepiercing mechanism of the main body unit 1 a of the micropore formingapparatus 1 is mainly configured by the chuck array 40, spring stopper50, release button 60, and main spring 80.

[Structure of Elements of the Main Body Unit]

As shown in FIGS. 2 and 3, a housing configured by the rear cover 10 andfront cover 20 is capable of accommodating therein the chuck array 40,spring stopper 50, release button 60, injector 70, main spring 80, andthe plurality of springs 90 a and 90 b. As shown in FIGS. 3 and 4, amounting part 11 for mounting the tip receiver insertion member 30 isformed at the bottom part of the rear cover 10. An opening 12 is formedat the top part of the rear cover 10 to expose a button part 72 of theinjector 70, and thus to allow a user to press the button part 72. Anopening 13 for exposing a button part 64 of the release button 60 isformed on the side surface of the rear cover 10. Within the rear cover10 are provided a concavity 14 into which is fitted one end part 52 a ofa spring receiver 52 of the spring stopper 50, a concavity 15 forengaging a support shaft 63 of the release button 60, a guide channel 16for guiding a guide part 43 of the chuck array 40 which moves in the Ydirection (vertical direction in FIGS. 1 through 5) within the housing,spring installation parts 17 and 18 for installing the springs 90 a and90 b, and four boss insert holes 19 for inserting the four bosses 27(refer to FIG. 5) of the front cover 20. Note that, in the presentembodiment, one end of the main spring 80 is held within the housing bya spring receiver 52 of the spring stopper 50.

As shown in FIGS. 3 and 5, the front cover 20, similar to the rear cover10, has a mounting part 21 for mounting the tip receiver insertionmember 30, an opening 22 for exposing the button part 72 of the injector70 and thus allow a user to press the button part 72, an opening 23 forexposing the button part 64 of the release button 60, a concavity 24into which is fitted the other end 52 b of the spring receiver 52 of thespring stopper 50, a concavity 25 for engaging the support shaft 63 ofthe release button 60, and a guide channel 26 for guiding the guide part43 of the chuck array 40 which moves within the housing in the Ydirection. Four bosses 27 are formed on the front cover 20 at positionscorresponding to the four boss insert holes 19 (refer to FIG. 3) of therear cover 10. Therefore, the front cover 20 can be positioned andmounted relative to the rear cover 10 by inserting the four bosses 27 ofthe front cover 20 into the boss insert holes 19 of the rear cover 10.

The tip receiver insertion member 30 is inserted through the tipreceiver 120 that accommodates the microneedle tip 110 duringinstallation of the microneedle tip 110 (refer to FIG. 11), and insertedthrough the empty tip receiver 120 when discarding the used microneedletip 110. As shown in FIGS. 3 and 6, the tip receiver insertion member 30includes a mounting part 31 for mounting the mounting part 11 of therear cover 10 and the mounting part 21 of the front cover 20, a contactsurface 32 for contacting the skin on the arm of a subject, a throughhole 33 that has an opening 33 a (refer to FIG. 6) formed on the contactsurface 32 and an opening 33 b (refer to FIG. 3) disposed on theopposite side thereof, and two flanges 34 formed so as to extend outwardfrom the outer surface in a lateral direction.

In the present embodiment, the opening 33 a formed on the side of thecontact surface 32 is configured such that the tip receiver 120 (referto FIG. 10), which accommodates the removable microneedle tip 110, isinsertable therein. The tip receiver 120 passes through the opening 33 aand can then travel in the Y direction through the through hole 33.

The chuck array 40 functions as a piston to cause the microneedle tip110 to strike or contact the skin of the subject, and is configured tobe movable in the Y direction along the guide channel 26 of the frontcover 20 and the guide channel 16 of the rear cover 10. The microneedletip 110 (refer to FIG. 11) being held in the chuck array 40 can travelin the Y direction through the tip receiver insertion member 30. Asshown in FIGS. 3 and 7, the chuck array 40 includes a main body 41provided with a plurality of holes 41 a to reduce weight, a pair ofelastically deformable chucks 42 for engaging the flanges 112 (refer toFIG. 12) of the microneedle tip 110 so as to hold the microneedle tip110, a guide part 43 a to be inserted into the guide channel 16 of therear cover 10, and a guide part 43 b to be inserted into the guidechannel 26 of the front cover 20, two connection parts 44 for engagingthe two fixed parts 62 of the release button 60 (to be described later),a convexity 45 having an insertion hole 45 a (refer to FIG. 3 forinserting a shaft 51 of the spring stopper 50 (to be described later),and a bushing part 46 formed on the bottom side (side in the arrow Y1direction) of the main body 41. The leading end 42 a of the chucks 42that abut the flange 112 of the microneedle tip 110 are tapered and havea hook shape allowing engagement with the flange 112.

In the present embodiment, when the two connection parts 44 do notengage the two fixed parts 62 of the release button 60 (to be describedlater), the chuck array 40 automatically holds the microneedle tip 110accommodated within the tip receiver 120 by inserting the microneedle110 (refer to FIG. 10) into the opening 33 a of the tip receiverinsertion member 30. Then, the chuck array 40, which is movable in the Ydirection, holds the microneedle tip 110, and thereafter moves to thearrow Y2 direction until the connection parts 44 are locked to the fixedparts 62.

Also in the present embodiment, when the two connection parts 44 do notengage the two fixed parts 62 of the release button 60 (to be describedlater), the microneedle tip 110 held by the chuck array 40 automaticallyremoves the tip receiver 120 from the chucks 42 of the chuck array 40 byinserting the tip receiver 120 into the opening 33 a of the tip receiverinsertion member 30.

In the present embodiment, the chucks 42 are integratedly formed ofsynthetic resin together with the other parts (main body 41, guide parts43 a and 43 b, connection parts 44, convexity 45, and bushing part 46).

The spring stopper 50 is provided to support the main spring 80 whichexerts a force on the chuck array 40 in the arrow Y1 direction. As shownin FIG. 3, the spring stopper 50 includes a shaft 51 to be insertedwithin the main spring 80, and a spring receiver 52 for preventing themain spring 80 from escaping upward (arrow Y2 direction) when the shaft51 is inserted in the main spring 80. The leading end part 52 a and theother end part 52 b of the spring receiver 52 are respectively fitted inthe concavity 14 of the rear cover 10 and the concavity 24 (refer toFIG. 5) of the front cover 20. In the present embodiment, a shortcylindrical shaped spacer 55 is provided to adjust the compressiondistance of the main spring 80 to the base of the shaft 51. One end 80 aof the main spring 80 (to be described later) abuts the bottom surfaceof the spacer 55. The length of the spacer 55 in the axial direction issuitably variable in accordance to the desired compression distance ofthe main spring 80. The spacer 55 can be omitted by adjusting the springconstant and length of the main spring 80.

As shown in FIGS. 3 and 8, the rear cover 10 is provided with a mainbody 61, two fixed parts 62 that engage the two connection parts 44 ofthe chuck array 40, two support shafts 63 for engaging the concavity 15of the rear cover 10 and the concavity 25 (refer to FIG. 5) of the frontcover 20, and a button part 64 that is exposed from the opening 13 inthe side surface of the rear cover 10 and the opening 23 (refer to FIG.5) in the side surface of the front cover 20. As shown in FIG. 8, theside surface of main body 61 that has the button part 64 is alsoprovided with a concavity 61 a accommodates one end of the spring 90 b(refer to FIG. 3) installed in the spring installation part 18 (refer toFIGS. 3 and 4) of the rear cover 10. In the present embodiment, the twofixed parts 62 function as stoppers that fix the chuck array 40 movingin the arrow Y2 direction against the force of the main spring 80 (to bedescribed later) exerted in the arrow Y1 direction, and maintain thechuck array 40 at the firing standby position.

In this embodiment, the ejector 70 has the function of discharging thetip receiver 120 that accommodates the microneedle tip 110 from thethrough hole 33 (refer to FIG. 3) of the tip receiver insertion member30. As shown in FIG. 3, the injector 70 is provided with a pressing part71 for pressing the edge part 121 b (refer to FIG. 10) and edge part 122d (refer to FIG. 14) of the tip receiver 120 (to be described later), abutton part 72 that is exposed from the opening 12 of the rear cover 10and the opening 22 of the front cover 20 so as to be pressable by theuser, and a contact part 73 that contacts one end of the spring 90 ainstalled in the spring installation part 17 of the rear cover 10. Aboss part 73 a to be inserted into the interior of the spring 90 a isformed on the contact part 73 to prevent the spring 90 a from beingremoved from the spring installation part 17 of the rear cover 10.

The main spring 80 is provided to exert a force on the chuck array 40 inthe arrow Y1 direction. As shown in FIG. 3, the shaft part 51 of thespring stopper 50 is inserted into the interior of the main spring 80.In this case, one end part 80 a of the main spring 80 contact the spacer55, and the spacer 55 contact the spring receiver 52 of the springstopper 50. The other end part 80 b of the main spring 80 contacts thetop surface of the connection part 44 of the chuck array 40. That is,the main spring 80, which is a force exerting means in the presentembodiment, is in a free state and neither end is fixedly attached toany other member.

When the spring 90 a is installed in the spring installation part 17 ofthe rear cover 10 and the boss part 73 a of the contact part 73 of theinjector 70 is inserted in the spring 90 a, the spring 90 a functions toexert a force on the injector 70 in the arrow Y1 direction when theinjector 70 is pushed in the arrow Y2 direction, as shown in FIG. 3.When the spring 90 b is installed in the spring installation part 18 ofthe rear cover 10 and disposed in the concavity 61 a (refer to FIG. 8)of the release button 60, the spring 90 b causes the release button 60,which has pivoted on the support shaft 63 in the arrow G2 direction, tothen rotate in the arrow G1 direction.

[Tip Receiver Kit]

The tip receiver kit 100, which is configured by the microneedle tip 110installed in the chuck array 40, the tip receiver 120 that accommodatesthe microneedle tip 110, and the sterilization seal 130, of themicropore forming apparatus 1 of the present embodiment is describedbelow in detail with reference to FIGS. 1, 3, 7, and 9 through 16.

The microneedle tip 110 is used when installed in the array chuck 40(refer to FIG. 7) of the previously described micropore formingapparatus 1, and has a plurality of microneedles 113 a for formingmicropores to extract interstitial fluid (fluid) from the skin of asubject. As shown in FIGS. 10 through 12, the microneedle tip 110 has arectangular shape when viewed from the planar aspect, and includes apair of protrusions 111 disposed so as to protrude to the outside fromthe exterior surface in a lateral direction, a pair of flanges 112disposed so as to protrude to the outside from the exterior surface in alongitudinal direction, a microneedle array 113 that has 305microneedles 113 a, and a concavity 114 into which is inserted thebushing part 46 (refer to FIG. 7) of the chuck array 40 of thepreviously described micropore forming apparatus 1. The pair ofprotrusions 111 are formed to lock to the locking holes 122 b of the tipreceiver 120 (to be described later), and the pair of flanges 112 areformed to engage the leading end part 42 a of the chuck 42 of the chuckarray 40 (refer to FIG. 7). Note that the microneedle tip 110 is made ofsynthetic resin and incorporates the 305 microneedles 113 a. Themicroneedles 113 a of the present embodiment have a conical shape withan apex angle of approximately 30 degrees, as shown in FIG. 12. Notethat a microneedle tip that incorporates a microneedle array portionwith 189 microneedles may also be used instead of the microneedle tip110 that incorporates the microneedle array 113 with the previouslymentioned 305 microneedles 113 a.

In the present embodiment, the synthetic resin tip receiver 120 includesthe opening 121 for receiving the sterile and unused microneedle tip 110(refer to FIG. 10), and the opening 122 for receiving the usedmicroneedle tip 110 that has been used to pierce the skin of a user, asshown in FIGS. 10 and 13 through 16. The opening 121 and the opening 122are provided on mutually opposite sides, and the sterilization seal 130(to be described later) is adhered to the opening 121 that accommodatesthe unused microneedle tip 110 in order to seal the opening 121. Asshown in FIGS. 10 and 13, the opening 121 has four supports 121 a forsupporting the side surface of the sterile and unused microneedle tip110, an edge part 121 b for contacting the pressing part 71 (refer toFIG. 3) of the injector 70, and a clearance part 121 c provided so thatthe protrusion 111 (refer to FIGS. 10 and 11) of the microneedle tip 110held by the support part 121 a does not touch the edge part 121 b.

In the present embodiment, the opening 122 includes a holder 122 a thathas a locking hole 122 b into which is inserted the protrusion 111(refer to FIGS. 10 and 11) of the used microneedle tip 110 that haspierced the skin of the user, as shown in FIGS. 14 and 15. The opening122 is provided with a release part 122 c for releasing the locked stateof the flange 112 of the microneedle tip 110 and the chuck 42 (refer toFIG. 7) of the chuck array 40 of the micropore forming apparatus 1, andthe edge part 122 d that contacts the pressing part 71 (refer to FIG. 3)of the injector 70. The leading end part 122 e of the release part 122 chas a tapered shape, as shown in FIG. 16. As shown in FIG. 14, thesymbol [2] is printed on the side surface 122 f of the tip receiver 120to allow confirmation that the opening 122 is on the top side.

The sterilization seal 130 is made of aluminum film, and functions toprevent viruses and bacteria from adhering to the microneedle tip 110which has been sterilized by gamma ray exposure or the like. As shown inFIGS. 9 and 10, the sterilization seal 130 is adhered so as to cover theopening 121 that accommodates the unused microneedle tip 110. Thesterilization seal 130 is also adhered so as to cover the symbol [2]printed on the side surface 122 f of the tip receiver 120 as previouslymentioned. As shown in FIG. 9, a symbol [1] is printed on the part ofthe seal adhered to the side surface 122 f of the tip receiver 120 so asto allow confirmation that the opening 121 is disposed on the top side.

In the present embodiment, when the locked state between the connectionpart 44 of the chuck array 40 and the fixed part 62 of the releasebutton 60 is released, the flange 112 of the microneedle tip 110 is heldby the chuck 42 of the chuck array 40 by the subject simply moving themicropore forming apparatus 1 so that the tip receiver 120 is insertedinto the opening 33 a of the tip receiver insertion member 30 byproviding the chuck array 40 to hold the microneedle tip 110 when thetip receiver 120 is inserted into the opening 33 a of the tip receiverinsertion member 30. At this time, the chuck array 40 can be fixedlyanchored by the fixed part 62 in the state of having moved in the Y2direction against force exerted by the main spring 80 on the chuck array40 at the same time the microneedle tip 110 is held by the chuck array40 by configuring the chuck array 40 so as to be movable in the Ydirection and by providing the fixed part 62 (release button 60) forengaging the connection part 44 of the chuck array 40 so as to fixedlysecure the chuck array 40. Thus, the subject can place the microporeforming apparatus 1 with the chuck array 40 held by the microneedle tip110 while in a state of being forced in the direction toward the skin(arrow Y2 direction) of the subject. The subject can therefore place themicropore forming apparatus 1 when the apparatus 1 is in a stead ofbeing ready to form micropores in the skin of the subject withoutrequiring complex operation by simply moving the micropore formingapparatus 1. In this state, micropores can be formed in the piercingregion of the skin of the subject by pressing the button part 66 of therelease button 60 to release the engagement between the connection part44 of the chuck array 40 and the fixed part 62 so as to move themicroneedle tip 110 in the arrow Y1 direction through the opening 33 aof the tip receiver insertion member 30.

In the present embodiment, when the microneedle tip 110 is held in thechuck array 40 and the engagement is released between the fixed part 62and the connection part 44 of the chuck array 40, the used microneedletip 110 held in the chuck array 40 can be easily removed when theconnection with the fixed part 62 has been released by the subjectsimply moving the micropore forming apparatus 1 so that the tip receiver120 is inserted into the opening 33 a of the tip receiver insertionmember 30 by inserting the empty tip receiver that does not accommodatea microneedle tip 110 into the opening 33 a of the tip receiverinsertion member 30. As a result, the subject can safely discard theused microneedle tip 110 without touching the used microneedle tip 110.

[Pressing the Microneedles into the Skin after Piercing]

In the present embodiment, when the microneedles 113 a of themicroneedle tip 110 have pierced the skin f the subject via the forceexerted by the main spring 80, the microneedles 113 a are maintained inthe state of piercing the skin and continue to be pressed to the skin ofthe subject by the force exerted by the main spring 80. Thus, the amountof interstitial fluid extracted from the micropores is increased and theaccuracy of the measurement using the extracted interstitial fluid isimproved. The pressing condition that is applied in the pierced state, afeature of the present invention, is described below.

FIG. 17 illustrates the principle of conventional piercing, and showsthe principle of conventional piercing in which the microneedles piercethe skin and are then removed from the skin of the subject. FIG. 18illustrates the principle of piercing in the present invention, andshows the microneedles piercing the skin of the subject and beingmaintained in that state for a predetermined time during which pressureis applied. Note that only the elements involved in the operation aredescribed and unnecessary elements are omitted from the description tofacilitate understanding.

FIG. 17(a) shows the normal state of a conventional micropore formingapparatus; a piston 200 is supported by a spring 201 used to draw thepiston 200, and the leading end of the microneedles 202 a of amicroneedle tip 202 installed in the leading end of the piston 200 aredischarged slightly from an opening 204 of a housing 203. A microneedledischarging spring 205 is in an uncompressed state at its full naturallength, and there is no force being exerted on the microneedles 202 a bythe microneedle discharging spring 205 in the direction toward the skin.

FIG. 17(b) shows the loaded state with the piston 200, moved from thestate shown in FIG. 17(a) in the non-piercing direction (the oppositedirection to the piercing direction, that is, upward in the drawing)with the microneedle discharging piston 205 compressed and maintainedthusly by the stopper 206. The piston 200 is separated from themicroneedle drawing spring 201, and the microneedles 202 a arecompletely accommodated within the housing 203. In this state, thedischarge preparation of the piston 200 is completed when the opening204 of the housing 203 contact the skin H of the subject.

FIG. 17(c) shows the state wherein the stopper 206 is released from thestate shown in FIG. 17(b), and the microneedles 202 a have beendischarged in the direction toward the skin by the force exerted by themicroneedle discharging spring 205. After the microneedles 202 a havepierced the skin H of the subject, the microneedles 202 a are instantlyretracted from the skin H via the force from the skin H and therepulsive force of the microneedle drawing spring 201 that wascompressed by the piston 200 when moving in the direction toward theskin.

FIG. 18(a) shows the normal state of the micropore forming apparatus ofthe present invention; although most of the leading end of themicroneedles 202 a are discharged from the opening 204 of the housing203, the microneedle discharging spring 205 is in an uncompressed stateat its full natural length and the microneedle discharging spring 205does not exert a force on the microneedles 202 a in the direction towardthe skin. Note that in FIG. 18(a) 207 refers to a short cylindricalspacer for adjusting the compression distance of the microneedledischarging spring 205 (corresponding to reference number 55 in FIG. 3),which is provided on the inner side of the housing 203.

FIG. 18(b) shows the loaded state with the piston 200, moved from thestate shown in FIG. 18(a) in the non-piercing direction with themicroneedle discharging spring 206 compressed and maintained thusly bythe stopper 206. In this case, the microneedles 202 a are completelyaccommodated within the housing 203. In this state, the dischargepreparation of the piston 200 is completed when the opening 204 of thehousing 203 contact the skin H of the subject.

FIG. 18(c) shows the state wherein the stopper 206 is released from thestate shown in FIG. 18(b), and the microneedles 202 a have beendischarged in the direction toward the skin by the force exerted by themicroneedle discharging spring 205. When the microneedles 202 a are inthe state of having pierced the skin H of the subject, the microneedledischarging spring 205 continues to exert a force that presses themicroneedles 202 a toward the skin. That is, the length, springconstant, and compression distance of the microneedle discharging spring205 are selected so as to provide this force using the previouslymentioned spacer 207 as desired. After the microneedles 202 a havepierced the skin H f the subject, the microneedles 202 a are stillpressed to the skin H by the force exerted microneedle dischargingspring 205 that is in excess of the force from the skin H.

[Effectiveness of Pressing after Piercing]

The effectiveness in increasing the amount of extracted interstitialfluid by pressing the microneedles into the skin after piercing wasverified by experiment. After the microneedles pierced the skin of thesubject, the microneedles were pressed for 5 seconds, 10 seconds, andseconds, then the glucose (Glc) transmittance was measured. The glucosetransmittance is an indicator of the amount of glucose extracted to theextraction medium per unit time (glucose extraction time: ng/min)standardized as a glucose value mg/dl. The method of measuring glucosetransmittance employs a resin chamber of 90 μL capacity, and filled withRO water (deionized water) as the extraction medium, disposed at thearea in which micropores have been formed and through which interstitialfluid passes to the epidermis of the forearm, such that the interstitialfluid is extracted to the chamber. Sampling was performed at 10 minuteintervals for 30 minutes. Then, 120 μL of RO water (deionized water) wasadded to the 90 μL of sampled extraction medium to produce a measurementsample, and the glucose concentration in the measurement sample wasanalyzed by a fluorescence method using an enzyme. Fluorescence wasmeasured using a microplate reader (MTP-800AFC; Corona Electric Co.) andglucose oxidase (Oriental Yeast Co.), ascorbic acid oxidase (Wako PureChemical Industries, Inc.), Amplex Red (Molecular Probes, Inc.),mutarotase (Oriental Yeast Co.), and Peroxidase (Wako Pure chemicalIndustries, Inc.) as reaction reagents. The glucose value was alsomeasured using a glucose auto analyzer and blood collected from theforearm.

Glucose transmittance was also measured by a conventional method(microneedles withdrawn from the skin immediately after piercing) forcomparison. the results are shown in FIG. 19. In FIG. 19, the box (□)symbol represents extraction with pressing after piercing (method of thepresent invention), and the triangle (▴) symbol represents extraction bythe conventional method (normal piercing). Note that although the box(□) symbol is plotted by the method of the present invention near thezero position of the pressing time, this position represents the bodilysensation pressing time of zero seconds (that is, when the microporeforming apparatus is removed from the skin immediately after the subjectfeels the piercing of the skin by the microneedles after the start ofthe piercing operation; the bodily sensation pressing time of thesubject is effectively zero seconds although normally 0.15 seconds isrequired to reach the operation of removing the micropore formingapparatus from the skin after the subject has felt the piercing).

It can be clearly understood from FIG. 19 that glucose transmittance isincreased by pressing the microneedles on the skin after piercing.Double the glucose transmittance of the conventional method was obtainedeven at a bodily sensation pressing time of zero seconds, andunderstandably the transmittance increased in accordance with theextension of the pressing time. Note that the time during which themicroneedles are pressed on the skin after piercing is preferably lessthan 60 seconds when considering the burden on the subject and reducingthe measurement time. However, the specific time of pressing themicroneedles on the skin after piercing is preferably 0.15 seconds orlonger when considering substantially increasing the transmittance evenat bodily sensation zero seconds (actually pressing for approximately0.15 seconds).

FIG. 20 shows the confirmed results transition of glucose transmittanceaccording to elapsed time after piercing by the conventional method(normal piercing) and the method of the present invention (pressedpiercing). The microneedle speed when striking the epidermal layerduring pressed piercing was 5 (m/s), and the pressing time afterpiercing was 1 minute. The microneedle speed when striking the epidermallayer during normal piercing was 6 (m/s). The extraction surface areawas 5×10 mm², and 90 μL of RO water was used as the extraction medium.It can be clearly understood from FIG. 20 that the method of the presentinvention, in which the microneedles were pressed on the skin afterpiercing, produced approximately 5 times the transmittance over the timecourse compared to forming micropores using a conventional piercingdevice.

[Transmittance and Damage]

From the perspective of improving accuracy, forming as many microporesas possible in the skin of the subject is preferable; however, whenconsidering the burden on the subject, it is preferable to reduce damagesuch as hemorrhage and pain associated with piercing.

Two subjects, subject A and subject B, were used in piercing tests underthe following conditions, and the relationship between glucosetransmittance and damage to the subject was verified. The results areshown in FIGS. 21 and 22.

[Test Conditions]

*Piercing: Piercing while pressing according to the present inventionand normal piercing (comparative example).

The microneedle speed when striking the epidermal layer during pressedpiercing was 5 (m/s), and the pressing time after piercing was thebodily sensation zero seconds. The microneedle speed when striking theepidermal layer during normal piercing was 8.5 (m/s).

*Number of Body areas: pressed piercing in 2 areas, and normal piercingin 3 areas.

*Extraction Conditions:

Extraction area: 5×10 mm²

Extraction Time: 10 minutes performed 3 times=30 minutes

Extraction Medium/Amount: RO water/90 μL

*Evaluation Items:

Transmittance: glucose (Glc) transmittance was measured

Damage: Pain, hemorrhage

FIG. 21 shows the relationship between glucose transmittance and pain.Subject pain was subjectively evaluated in 10 relative levels. It can beunderstood from FIG. 21 that pain by pressed piercing was equal to orless than that by normal piercing, and glucose transmittance was high.FIG. 22 shows the relationship between glucose transmittance andhemorrhage. Although hemorrhage may occur from micropores formed bypiercing, the number of such locations were visually counted by thenumber of small hemorrhagic red dots observed in the microneedle area ofthe microneedle array. It can be understood from FIG. 22 that althoughno hemorrhages were observed by pressed piercing, the glucosetransmittance was greater than that by normal piercing.

[Pressing Force and Damage]

An aspect of the present invention is pressing the microneedles towardthe skin after piercing, and whether the force exerted in pressing themicroneedles toward the skin influenced pain and hemorrhage wasinvestigated. The pressing pressure (pa) of the microneedles toward theskin was changed by changing the compression distance (mm) of thedischarge spring exerting a force on the microneedles on the skin. Thepressing force toward the skin increased as the discharge springcompression distance increased. The results are shown in Tables 1 and 2.Table 1 shows the relationship between pain and pressing force, andTable 2 shows the relationship between hemorrhage and pressing force.

In Table 1, [Pressing Only] is defined as manually holding themicroneedle tip under a state of force exerted by the discharge spring,with the microneedles of the microneedle tip contacting the specimenskin at low speed (0.6 m/s), and the microneedles pressing the skin viathe force exerted by the discharge spring. [Discharge and Pressing] isdefined as moving the piston to the skin side by releasing the stopperin the loaded state shown in FIG. 18(b) so that the microneedles strikethe skin, and pressing the microneedles on the skin via the forceexerted by the discharge spring after piercing.

TABLE 1 Discharge spring compression Pressing Only Discharge andPressing distance (mm) Specimen 1 Specimen 2 Specimen 1 Specimen 2 8 Nopain No pain No pain No pain 10 No pain No pain No pain No pain 11 Nopain No pain Pain Pain

TABLE 2 Discharge Spring Compression Pressing Only Discharge andPressing Distance (mm) Specimen 1 Specimen 2 Specimen 1 Specimen 2 8 NoNo No No Hemorrhage Hemorrhage Hemorrhage Hemorrhage 10 No No No NoHemorrhage Hemorrhage Hemorrhage Hemorrhage 11 No No No No HemorrhageHemorrhage Hemorrhage Hemorrhage

According to Table 1, there was no change in the evaluation of [PressingOnly] as [No Pain] even when the pressing force was increased byincreasing the compression distance of the discharge spring to 8 mm, 10mm, and 11 mm. The only cases resulting in [Pain] for [Discharge andPressing] were at discharge spring compression distance of 11 mm. Thus,the subject's sensation of pain is influenced by the striking speed(piercing speed) of the microneedles on the skin, whereas pressing themicroneedles on the skin after piercing does not result in pain.

According to Table 2, there was no hemorrhage for either [Pressing Only]or [Discharge and Pressing] even when the discharge spring compressiondistance was increased to 8 mm, 10 mm, and 11 mm, and neither didpressing force affect hemorrhage.

The micropore forming method of the present invention presses themicroneedles on the skin for a predetermined time after the microneedleshave pierced the skin, and a force is exerted by the discharge spring sothat the microneedles are not withdrawn from the skin after piercing.When the exerted force is increased so as to have excessive strikingspeed on the skin surface, the subject experiences pain. Therefore, thespeed of the microneedles striking the skin surface and the forceexerted on the microneedles on the skin should be in a preferred range.This range will differ depending on microneedle specifications (shape,number, material and the like), and examples are described below basedon Table 3.

TABLE 3 Discharge Spring Compression Pressing Piercing Distance forcemicroneedle Speed [mm] [Pa] Behavior [m/s] Pain Hemorrhage 2.5 1667microneedle 4 No No Withdrawal From pain Hemorrhage Skin After Piercing5 140000 microneedle 4.6 No No Withdrawal From pain Hemorrhage SkinAfter Piercing 6 212000 microneedle 4.7 No No Withdrawal From painHemorrhage Skin After Piercing 7 256000 microneedle Not 4.8 No NoWithdrawn from pain Hemorrhage Skin After Piercing 8 306000 microneedleNot 4.9 No No Withdrawn from pain Hemorrhage Skin After Piercing 10416667 microneedle Not 6.1 No No Withdrawn from pain Hemorrhage SkinAfter Piercing 11 472000 microneedle Not 6.7 Pain No Withdrawn fromHemorrhage Skin After Piercing

The microneedles of Table 3 were 305 microneedles made of syntheticresin covering a rectangular region (5×10 mm) as shown in FIGS. 11 and12. The microneedles were conical and the apex angle was 30 degrees. Thedischarge spring compression distance was changed by changing the sizeof the spacer (refer to FIG. 18 in contact with one end (the oppositeend from that on the subject skin side) of the discharge spring. Thebehavior of the microneedles (whether withdrawn from the skin afterpiercing) and presence of pain and hemorrhage were evaluated.

In the examples shown in Table 3, the microneedles were withdrawn fromthe skin after piercing when the piercing speed was 4.7 m/s, and themicroneedles were not withdrawn from the skin after piercing when thepiercing speed was 4.8 m/s. It is therefore preferable that themicroneedles strike the skin at a speed of 4.8 m/s or more. However, thesubject experienced pain when the piercing speed was 6.7 m/s, and thesubject did not feel pain when the piercing speed was 6.1 m/s.Therefore, it is preferable that the speed at which the microneedlesstrike the skin is 6.1 m/s or less.

The microneedles were withdrawn from the skin after striking when thepressing force was 2.12×10^(<5) (Pa), but the microneedles were notwithdrawn from the skin after striking the skin when the pressing forcewas 2.56×10^(<5) (Pa). Therefore the microneedle pressing force ispreferably 2.56×10⁵ (Pa) or more.

[Modifications]

Note that the present invention is not limited to the previouslydescribed embodiment and may be variously modified. For example, theshape of the members configuring the chuck array, that is, the skincontact part, and the method of installing the main spring, that is, theforce exerting means, may be variously modified.

Although 305 conical microneedles are arranged in a rectangular regionas the microneedle tip in the above embodiment, the number, shape andmaterial of the microneedles as well as the shape of the microneedle tipprovided with these microneedles may be variously modified.

Although only a main spring for exerting a force on the chuck array inthe piercing direction is used as the means for exerting a force on thechuck array in the above embodiment, a pressing spring that has a smallspring constant may be disposed in the guide channel of the rear coverand in the guide channel of the front cover to prevent the leading endof the microneedles from protruding outside from the opening of the tipreceiver installation member when the micropore forming apparatus isremoved from the skin of the subject after piercing and after completionof the pressing operation. In this case, the specifications of thelength and spring constant of the main spring must be selected so as toprovide a force to press the microneedles on the skin when the guidepart has compressed the pushing spring and the microneedles have struckthe skin.

The micropore forming apparatus also may be provided with a timer toalert the subject to the length of time the microneedles have beenpressed on the skin. In this case, a timer power source can be turned ONby the operation of installing the microneedle tip in the chuck arrayand moving the chuck array to the discharge position, and the timer canbe started by the discharge of the chuck array.

What is claimed is:
 1. A micropore forming apparatus for formingmicropores in the skin by piercing the skin of a subject withmicroneedles comprising: a skin contact part that has a plurality ofmicroneedles for piercing the skin of the subject; and a spring forexerting a force on the skin contact part toward the skin of thesubject; wherein the spring has a length so as to maintain the state ofcompression of the spring and thereby maintain the state of themicroneedles being pressed into the skin after the microneedles haveinitially pierced the skin of the subject, wherein, after themicroneedles have pierced the skin, the spring exerts a force P (Pa) onthe skin through the microneedles such that 2.56×10⁵≦P.
 2. The microporeforming apparatus of claim 1, wherein the speed S (m/s) of themicroneedles piercing the skin is set such that 4.8≦S.
 3. The microporeforming apparatus of claim 1, wherein the speed S (m/s) of themicroneedles piercing the skin is set such that S is ≦6.1.
 4. Amicropore forming method for forming micropores in the skin of a subjectusing a micropore forming apparatus for forming micropores in the skinby piercing the skin of the subject with microneedles; wherein themicropore forming apparatus comprises: a skin contact part that has aplurality of microneedles for piercing the skin of the subject; and aspring for exerting a force on the skin contact part toward the skin ofthe subject; wherein the spring has a length so as to maintain the stateof compression of the spring and thereby maintain the state of themicroneedles being pressed into the skin after the microneedles haveinitially pierced the skin of the subject, the method further comprisingcollecting interstitial fluid extracted from the micropores by anextraction medium.
 5. The micropore forming method of claim 4, whereinthe predetermined time is 0.15 second or longer.
 6. The microporeforming method of claim 5, wherein the predetermined time is 60 secondsor less.
 7. The micropore forming method of claim 4, wherein the speed S(m/s) of the microneedles piercing the skin is set such that 4.8≦S. 8.The micropore forming method of claim 4, wherein the speed S (m/s) ofthe microneedles piercing the skin is set such that S≦6.1.
 9. Themicropore forming method of claim 4, wherein, after the microneedleshave pierced the skin, the spring exerts a force P (Pa) on the skinthrough the microneedles such that 2.56×10⁵≦P.